1. Field of the Invention
The present invention relates generally to cables and more particularly to cables for use in an earth formation traversed by a borehole.
2. Background Information
Gathering petrophysical, geophysical and well production information using various techniques is well known and widely practiced. Various types of geophysical and petrophysical measurements as well as well production measurements are known in the art. These measurements are typically performed downhole within the earth formation requiring transmission of signals, such as power and data, between the power supply and data acquisition equipment, typically located at the surface, and a downhole sensor by way of which the measurement is performed. The transmission of signals is done through special electrical cables. Such cables have to withstand severe conditions found downhole such as high temperatures, high pressure, shear forces etc.
A conventional cable 100 that may be used in the above applications is shown in FIG. 1. Cable 100 includes a plurality of conductors 102 that conduct signals therethrough. Each conductor is covered with a layer 103 of suitable insulation material. Cable 100 also includes bumper cables 104 positioned on both sides of conductors 102. The conductors 102 and bumper cables 104 are encapsulated by way of a jacket of insulating material 106 that maintains them in place and protects them from interaction with different agents existing downhole. The bumper cables 104 serve the purpose of protecting conductors 102 as well as of supporting the weight of cable 100. Because the depth of the well requires cables that are quite long, these cables may be very heavy and oftentimes cannot support their own weight without the bumper cables.
Cable 100 described above suffers of various disadvantages. The presence of the bumper cables 104 increases the likelihood of a short circuit. Also the bumper cables are quite heavy, making the overall cable heavy. Furthermore, the bumper cables have a relatively large diameter, which makes the size of cable 100 quite large. As the space in the borehole is limited, a larger size cable increases the risk of cable failure due to the various shear forces that may be exerted thereon. It is desirable to provide a cable for use in downhole applications that does not suffer of the above-mentioned disadvantages.